Electric strike

ABSTRACT

An electrically operated strike for coacting with a bolt of a door lock includes a casing adapted to be mounted on a door frame and a bolt member slidable between a projected position engaging the door lock bolt, and a retracted position. Spring means are provided for biasing the bolt member toward the projected position and a solenoid is provided for effecting movement of the bolt member against the biasing effect of the spring to its retracted position. Dogging means are interconnected between the solenoid and the bolt member and have a dogging position holding the bolt member in its projected position when the solenoid is not energized and a release position providing for movement of the bolt member to its retracted position when the solenoid is energized. The dogging means is operable when in its dogging position to transfer external forces applied to the bolt member to the casing to thereby render the external forces ineffective to move the bolt member toward its retracted position.

Waited States Patent 1 Balzano 1 July 31, 1973 1 ELECTRIC STRIKE [57] ABSTRACT [75] Inventor: Alfie) Balzano Anaheim Calif An electrically operated strike for coacting with a bolt [73] Assignee: Eaton Corporation, Cleveland, Ohio of a door lock includes a casing adapted to be mounted on a door frame and a bolt member slidable between [22] May 1971 a projected position engaging the door lock bolt, and

[21 A No; 145,672 a retracted position. Spring means are provided for biasing the bolt member toward the projected position and a solenoid is provided for effecting movement of [52] US. Cl. the bolt member against the biasing effect of the spring [51] hit. Cl. lc6 If to its retracted position Dogging means are intercom [58] F em or 25 b nected between the solenoid and the bolt member and l I have a dogging position holding the bolt member in its projected position when the solenoid is not energized [56] References Cited and a release position providing for movement of the UNITED STATES PATENTS bolt member to its retracted position when the solenoid 3,083,562 4/1963 Weizer 292/34Ll6 X is energized. The dogging means is operable when in its 2,691,544 10/1954 Park er 292/254 do ing position to transfer external forces applied to 3,638,984 2/1972 DaYldson 29254116 the bolt member to the casing to thereby render the ex- 3,l52,826 10/1964 Smith 292/341.16 temal forces ineffective to move the bolt member Primary Examiner-Richard E. Moore Attarney-Teagno 8L Toddy ward its retracted position.

11 Claims, 7 Drawing Figures PAIENIEUJUW m3 SHEET 1 OF 2 3y 4 dw- A TTORNEYS x 3 40 l I ELECTRIC STRIKE This invention relates to strikes for door locks, and more particularly to a novel strike of the class that is electrically operated.

Those skilled in the art will appreciate that the strikes of this class comprise a retractable catch or strike member that is mounted on a door frame for engaging the bolt of a lock on the door. The strike member or catch of the strike is retracted electrically to permit the door to open, and must resist attempts to retract it by externally applied force or manipulation. Due to limitations of space and other design considerations, the amount of operating power that can be applied is relatively small. Nevertheless, the strike should operate without fail while also being able to withstand attacks by unauthorized persons. All of this has caused serious problems in the design of electrically operated strikes.

The designers of the prior art generally have thought that an electrically operated strike should engage the lock bolt through a catch that rotates. In some instances the prior art merely utilizes a catch that is rotated to a retracted position by the bolt of the door lock when the door opens, the catch merely being controlled by a solenoid operated dog. In other instances, the solenoid acts to rotate the catch, first moving a dog to release the catch. Actually, the prior art contains many examples of electrically operated strikes, but those strikes have not been fully satisfactory because it has been found that it is possible through certain procedures, such as rapping, to release the catch of the strike. There is an increasing need for security and many persons today equip doors with locks of high quality, but the lock obviously is of little consequence when it is used with a strike that is not secure. Through the novel concept of my invention, I am able to construct an electrically operated strike that will operate extremely well, while also offering a high degree of security.

Accordingly, an object of the present invention, is to provide a strike with a bolt member that will slide in a linear direction on the strike casing for coacting with the bolt of the lock. A solenoid is mounted in the casing and has a spring pressed plunger that presses the bolt member linearly to a projected position. The solenoid upon energization slides the bolt member to a retracted position releasing the bolt of the lock. Dogging means are provided engaging between the bolt member and the strike casing, and acting to dog the bolt member each time the member slides to a projected position. Particularly, the dogging means provides surfaces through which the spring pressure of the solenoid plunger will act to maintain the dogging means in dogging position, effectively holding the bolt member in its projected position despite external forces that may be applied to the strike.

Preferably, the solenoid is mounted to act in a direction that is aligned relatively to the linear sliding of the bolt member on the strike. Moreover, as a further feature the dogging means is formed with surfaces interlocking so as to accept the external forces that may be applied to the bolt member, while transferring a part of those forces in a transverse direction binding parts of the strike to one another.

Another object of the present invention is to provide a new and improved electrically operated strike for coacting with a bolt of a door lock including a casing adapted to be mounted on a door frame, a bolt member slidable between a projected position engaging the bolt of the door lock and a retracted position releasing the bolt of the lock, spring means biasing the bolt member toward the projected position, electrical means effective when energized to move the bolt member against the biasing effect of the spring means to the retracted position, and interconnecting means interconnecting the bolt member and the electrical means, the interconnecting means having a dogging position for holding the bolt member in the projected position, and a release position providing for movement of the bolt member to the retracted position, the interconnecting means when in the dogging position act to transfer external forces applied to the bolt in a transverse direction toward the casing to render the external forces ineffective to move the bolt to the retracted position, and wherein the electrical means effects movement of the interconnecting means to the release position upon energization of the electrical means.

Further objects and advantages of the present invention will become apparent from the following dscription of preferred embodiments thereof taken in conjunction with the following drawings wherein:

FIG. 1 is a sectional view of one embodiment of the electric strike of the present invention;

FIG. 2 is a partially longitudinal sectioned view taken approximately along the lines 2-2 of FIG. 1 and showing the door and door bolt in phantom lines;

FIG. 3 is a cross sectional view taken approximately along the line 3-3 of FIG. 1 more fully illustrating the dogging means;

FIG. 4 is a view similar to the view illustrated in FIG. 1 showing the strike in a retracted condition;

FIG. 5 is a longitudinal sectional view of another embodiment of the electric strike of the present invention;

FIG. 6 is a cross sectional view taken approximately along the line 6--6 of FIG. 5 more fully illustrating the dogging means; and

FIG. 7 is a longitudinal sectional view similar to the view illustrated in FIG. 5 and illustrating the bolt of the strike in a retracted position.

Referring now more particularly to, FIG. 1 of the drawings, the electric door strike ,10 includes a bolt member 12 and a casing 14. The casing 14 is adapted to be mounted in a well known manner in the frame of a door and the bolt member 12 is positioned so'as to engage the bolt 16 of the door lock, illustrated in phantom lines in FIG. 2, in a well known manner to prevent relative movement between the door and the bolt member 12 of the electric strike 10. The bolt member 12includes a roller 13 located at one end thereof to provide for smooth cooperation of the bolt 12 and the bolt 16 of the door lock. Where the lock is equipped with a deadlatching guard bolt 16a, the bolt member 12 or its roller 13 will hold guard bolt 16a depressed as will be understood by those skilled in the art.

A solenoid 18 having a coil 20 and a plunger 22 is provided to effect movement of the bolt 12 from its projected position shown in FIG. I to its retracted position illustrated in FIG. 4 upon energization of the solenoid 18. The casing 14 has a screw 15 engaging a slot 17 in bolt member 12 whereby to form a limit stop for the projecting and retracting movements of member 12. A spring 24 is provided to bias the plunger member 22 outwardly from the coil 20 of the. solenoid 18. The spring 24 engages with an annular shoulder portion 26 disposed on the plunger member 22 and with a plate 28 of the casing 14. The spring 24 is an expansion spring and acts to bias the plunger member 22 outwardly from the coil 20. Energization of the coil will effect the movement of the plunger member 22 inwardly thereof against the force of spring 24 to effect movement of the bolt 12 to its retracted position illustrated in FIG. 4 as will be more fully described hereinbelow.

Dogging means 30 is provided interconnecting the plunger member 22 and the bolt 12. The dogging means acts to effect movement of the bolt 12 to its retracted position upon movement of the plunger member 22 inwardly of the coil 20. The dogging means 30 also cooperates with the casing 14 to prevent movement of the bolt 12 toward its retracted position when the solenoid 18 is not energized. The dogging means 30 includes a plate 32 pivotably supported by a pivot pin 34 which extends through an opening 36 in the plate 32 and into the bolt member 12. The pivot pin 34 enables the plate 32 to rotate relative to the bolt 12. The plate 32 includes an elongate opening 38 which engages a pin 40. The pin 40 is fixed to the plunger member 22 and cooperates with the elongate opening 38 to form a lost motion connection between the plunger 22 and the bolt 12. The pin 40 and a cam surface 39 of opening 38 also cooperate to form cam means for biasing the dogging means 30 into a condition preventing movement of the bolt 12 to its retracted position when the solenoid 18 is not energized. The plate 32 includes a projecting arm portion 42 having a shoulder portion 44 thereon. The shoulder portion 44 is adapted to engage with a groove 46 disposed in the casing 14 when the bolt is in its projected position.

When the bolt 12 is in its projected position the spring 24 will act to continually bias the shoulder 44 of the plate 32 into engagement with the groove 46. The spring 24 exerts a force on the plunger 22 in a direction parallel to the longitudinal axis of the plunger 22 and the bolt 12. The force of the spring 24 is transferred to the plate 32 by the pin which is fixed to the plunger 22 and which moves therewith. The pin 40 which is biased by the spring 24, transfers the force of the spring to the cam surface 39. The cam surface 39 and pin 40 act to bias the plate 32 in a clockwise direction about the pin 34. Thus, the force of the spring 24 acts to continuously bias the plate 32 in a clockwise direction when the solenoid 18 is not energized to thereby maintain the shoulder portion 44 of the plate 32 in engagement with the groove 46 in the casing 14.

The shoulder portion 44 cooperates with the groove 46 in the casing 14 to hold the bolt member 12 in its projected position. Thus, external forces that may tend to effect relative movement of the bolt 12 toward its retracted position will be applied through pivot pin 34 to the plate 32, while the spring pressure of plunger 22 acts in an opposed direction through pin 40 on plate 32 to press shoulder 44 against groove 46 on the casing. Thereby shoulder 44 will transfer the external forces in a transverse direction to the casing 14. Procedures such as rapping, where an external pressure is maintained on the bolt while blows are applied to the strike or door frame, will not shift the bolt member 12 from its projected position, due to the fact that the forces acting will merely bind the bolt member to its casing.

When the solenoid 18 is energized, the plunger 22 moves against the force of the spring 24 and the pin 40 first acts on the opening 38 in the plate 32 to pivot the plate 32 in a counterclockwise direction about the pivot pin 34, thereby removing the shoulder portion 44 from the groove 46 and permitting a movement of the bolt 12 to its retracted position. It should be apparent that the pin 40 and opening 38 form a lost motion connection which enables the shoulder 44 to be removed from the groove 46 prior to movement of the bolt 12 inwardly of the casing 14. After the plate 32 has been pivoted by the linear movement of the pin 40, the pin 40 engages with the end portion of the opening 38, as is illustrated in FIG. 4, so that further linear movement of the plunger 22 will effect movement of the bolt 12 to its retracted position asis shown in FIG. 4.

The electric door strike 10 will offer very high security requiring that solenoid 18 be energized before bolt member 12 can move to its retracted position. The dogging means 30 increase the security of the device by transferring external forces acting on the bolt 12 in a transverse direction toward the casing 14. Moreover, the spring 24 cooperates with the opening 38 and pin 40 to continuously urge the dogging means 30 into a condition in which movement of the bolt 12 to its retracted position cannot be effected unless the solenoid 18 is energized. Even rapping" of the door frame while applying pressure to the bolt 12 will be ineffective to compromise the security of the device.

FIGS. 5 to 7 illustrate a further form of the present invention in an electric door strike 50. The strike 50 includes a bolt member 52 and a casing 54. A solenoid 56 is provided for effecting linear sliding movement of the bolt 52 from its projecting position illustrated in FIG. 5 to its retracted position illustrated in FIG. 7. The solenoid 56 includes coil 62, a plunger 58 and a spring 60. The spring 60 abuts against a shoulder portion 6! disposed on the coil 62 of the solenoid 56 and against an annular shoulder portion 64 disposed on the plunger member 58 to bias the plunger member 58 outwardly from the solenoid 56 when the coil 62 is not energized. A pin 53 is disposed in the bolt 52 and engages a slot 55 inside of the casing 54, so that slot 55 will form a limit stop for the sliding of the bolt member 52 and will limit its movements at projected and retracted positions relative to the casing 54.

interconnecting the plunger member 58 and the bolt member 52 is dogging means 66. The clogging means 66 include a plate member 68 attached by a pin 71 to the end of the plunger member 58 so as to move integrally therewith. The plate member 68 cooperates with a plate member which is pivotably'supported by a pin 72 which is fixed to the casing 54. The plate member 70 includes a shoulder portion 74 which engages with a shoulder portion 76 of the plate-member 68, and a shoulder portion 78 which engages a rearward surface portion 80 of the bolt member 52.

When the bolt member 52 is in its projected position as is illustrated in FIG. 5 the dogging means 66 prevents movement of the bolt member 52 toward its retracted position. That will be understood when it is seen that the plate 68 prevents rotation of the plate 70 about the pivot pin 72 by the engagement of the cooperating portions 74 and 76 of the plates 70 and 68 respectively. External forces applied to the bolt member 52 cannot then eflect movement of the bolt member inwardly of the casing 54 due to the fact that the engagement between shoulders 78 and 80 on the plate 70 and bolt member 52 respectively will hold the bolt member 52 in its projected position. More in detail the external forces acting on the bolt member 52 will tend to rotate the plate 70, which will transfer those forces in a transverse direction through the portions 74 and 76 and the plate 68 to a side wall of the casing 54. In other words, the side wall of the casing 54 will effectively oppose a movement of bolt member 52 toward its retracted position.

Upon energization of the solenoid 56, the plunger member 58 will move inwardly against the biasing force of the spring 60. Inward motion of the plunger member 58 will effect movement of the plate 68 relative to the bolt member 52 until the plate 68 engages with the pins 82 disposed on the bolt member 52 as is shown in FIG. 7. When the plate 68 has engaged with the pins 82, the shoulder portions 74 and 76 of the plates 70 and 68, respectively, will no longer be in engagement and the plate 70 will be free to rotate about the pivot pin 72. Further movement of the plunger 58 inwardly of the solenoid 56 will effect movement of the bolt member 52 due to the fact that the plate 70 will no longer oppose retracting movement of the bolt member 52.

It should be apparent that the pins 82 and the plate 68 form a lost motion connection in that initial movement of the plate 68 and plunger 58 will not effect movement of the bolt member 52. After the plunger 58 has moved so that the plate 68 has moved to engage with the pins 82, further movement of the plunger member 58 inwardly of the solenoid 56 will effect movement of the bolt member 52. Movement of the bolt 52 toward the retracted position will effect pivotal movement of the plate 72 by a force exerted on the shoulder portion 78 thereof by the surface 80 of the bolt member 52, as is illustrated in FIG. 7.

It should be apparent that the embodiment of the invention illustrated in FIGS. 55-7 comprises dogging means 66 which transfers external forces that may be exerted on the bolt member 52, when the solenoid is not energized, in a transverse direction to the casing 54 of the electric strike 50. The dogging means 66 thus will prevent movement of the bolt 52 to its retracted position at all times when the solenoid 56 is not energized. The embodiment illustrated in FIGS. 5-7 will utilize the contribution of the present invention to offer a high degree of security, in much the same way as has been described in connection with FIGS. 1-4.

From the foregoing, it should be apparent that the concept of the invention makes it possible to construct an electric strike that will operate very well, while being able to resist attack much better than has been the ease with the electric strikes of the prior art. it is believed that the very considerable value of the invention will be understood, and that its merits will be fully appreciated by those skilled in the art.

I now claim:

' 1. An electrically operated strike adapted to be mounted on a door frame for controlling opening movements of a door and comprising a casing, a bolt member mounted in said casing and slidable relative thereto between a projected position for engaging a part on the door and a retracted position releasing the part on the door, said casing including a guide surface limiting the movement of said bolt member to a substantially linear direction, spring means biasing said bolt member toward said projected position, electrical means effective when energized to slide said bolt member against the biasing effect of said spring means to said retracted position, and interconnecting means interconnecting said bolt member and said electrical means for sliding said bolt member and through which said spring means and said electrical means act relative to said bolt member, said interconnecting means including dogging means having a dogging position holding said bolt member in said projected position and a release position permitting said bolt member to move toward said retracted position, said dogging means when in said dogging position acting to transfer external forces that may be applied in retracting direction to said bolt member to said casing in a direction transverse to said retracting direction to thereby render said external forces ineffective to retract said bolt member, said electrical means being operable to effect movement of said dogging means to said release position to thereby enable said bolt member to move to said retracted position, said dogging means including a plate member pivotably attached to said bolt member and a groove disposed in said casing, said plate member including a shoulder portion engaging said groove when said dogging means is in said dogging position to transfer forces exerted on said bolt member in a transverse direction toward said casing, said plate member being pivotable when said dogging means is in said release position to effect disengagement of said groove and said shoulder portion of said plate member to permit movement of said plate member with said bolt member toward said retracted position.

2. An electrically operated strike as defined in claim 1 wherein said electrical means includes a solenoid having a plunger and spring means for biasing said plunger toward said bolt and said dogging means further includes a pin attached to said plunger member and movable therewith and an opening disposed in said plate member and through which said pin extends, said spring means biasing said plunger and said pin to engage said opening to pivotably bias said plate member in a first direction to position said shoulder of said plate member in engagement with said groove when said solenoid is deenergized, said pin engaging with said opening and effecting rotation of said plate member in a direction opposite said first direction to remove said shoulder from said groove upon energization of said solenoid to prevent movement of said bolt member inwardly of said casing.

3. An electrically operated strike as defined in claim 2 further including a stop member disposed in said casing and an opening disposed in said bolt member, said stop member extending into said opening in said bolt member and acting to limit movement of said bolt member between said projected position and said retracted position. I Y 4 4. An electrically operated strike adapted to be mounted on a door frame for controlling opening movements of a door and comprising a casing, a bolt member mounted in said casing and slidable relative thereto between a projected position for engaging a part on the door and a retracted position releasing the part on the door; said casing including'a guide surface limiting the movement of said bolt member to a substantially linear direction, spring means biasing said bolt member toward said projected position, electrical means effective when energized to slide said bolt member against the biasing effect of said spring means to said retracted position, and interconnecting means interconnecting said bolt member and said electrical means for sliding said bolt member and through which said spring means and said electrical means act relative to said bolt member, said electrical means including a solenoid having a plunger and a spring for biasing said plunger toward said bolt member when said solenoid is deenergized, said interconnecting means including dogging means having a dogging position holding said bolt member in said projected position and a release position permitting said bolt member to move toward said retracted position, said dogging means when in said dogging position acting to transfer external forces that may be applied in retracting direction to said bolt member to said casing in a direction transverse to said retracting direction to thereby render said external forces ineffective to retract said bolt member, said electrical means being operable to effect movement of said dogging means to said release position to thereby enable said bolt member to move to said retracted position, said dogging means including a first plate member attached to said plunger and movable therewith, and a second plate member pivotably mounted on said casing, said second plate being disposed between said first plate member and said bolt member and having a first surface engageable with said bolt member and a second surface opposite said first surface for engaging with said first plate member, said first plate member preventing rotation of said second plate member and acting to hold said first surface of said second plate member in engagement with said bolt member to prevent movement of said bolt member toward said retracted position when said solenoid is deenergized, said first plate member disengaging with said second plate member to enable said second plate member to rotate upon energization of said solenoid to enable said bolt member to move toward said retracted position.

5. An electrically operated strike as defined in claim 4 further including a stop member attached to said bolt member and an opening disposed in said casing, said stop member cooperating with said opening to limit movement of said bolt member between said projecting and retracted positions.

6. In an electrically operated strike for coacting with a bolt of a door lock, a casing adapted to be mounted on a door frame, a bolt member slidable relatively to a projected position on the casing for engaging the bolt of the door lock, said casing having guide surfaces that support the bolt member for movements in a linear direction while sliding on the casing, a solenoid mounted on said casing and equipped with a spring pressed plunger normally pressing the bolt member to its projected position and sliding the bolt member on its guide surfaces to a retracted position when the solenoid is energized, dogging means movable to position engaging between the bolt member and the casing to dog the bolt member in its projected position, connecting means whereby the solenoid plunger moves the dogging means to dogging position each time the plunger slides the bolt member to projected position, and comprising surfaces through which the spring pressure of the plunger acts to hold said dogging means in dogging position, so that external forces that may be applied to the strike or its bolt member will be ineffective to release the bolt member for sliding away from projected posi tion, the solenoid plunger being effective by said connecting means to move the dogging means to release position when its plunger moves to retract the bolt member.

7. In an electrically operated strike as defined in claim 6 wherein said dogging means include a plate member pivotably attached to said bolt member and a groove disposed in said casing, said plate member including a shoulder portion engaging said groove when said dogging means is in said dogging position to transfer forces exerted on said bolt member in a transverse direction toward said casing, said plate member being pivotable when said dogging means is in said release position to effect disengagement of said groove and said shoulder portion of said plate member to prevent movement of said plate member with said bolt member toward said retracted position.

8. In an electrically operated strike as defined in claim 7 wherein said connecting means includes a pin attached to said solenoid plunger and movable therewith and an opening disposed in said plate member and through which said pin extends, said spring pressed plunger acting to bias said pin to engage said opening to pivotably bias said plate member in a first direction to position said shoulder of said plate member in engagement with said groove when said solenoid is deenergized, said pin engaging with said opening and effecting rotation of said plate member in a direction opposite said first direction to remove said shoulder from said groove upon energization of said solenoid to permit movement of said bolt member inwardly of said casing.

9. In an electrically operated strike as defined in claim 8 further including a stop member disposed in said casing and an opening disposed in said bolt member, said stop member extending into said opening in said bolt member and acting to limit movement of said bolt member between said projected position and said retracted position.

10. In an electrically operated strike as defined in claim 8 wherein said dogging means includes a first plate member attached to said solenoid plunger and movable therewith, and a second plate member pivotably mounted on said casing,,said second plate member being disposed between said first plate member and said bolt member and having a first surface engageable with said bolt member and a second surface opposite said first surface for engaging with said first plate member, said first plate member preventing rotation of said second plate member and acting to hold said first sur-,

face of said second plate member in engagement with said bolt member to prevent movement of said bolt member toward said retracted position when said solenoid isdeenergized, said firstplate member disengag ing with said second plate member to enable said second plate member to rotate upon energization of said solenoid to enable said bolt member to move toward said retracted position.

11. In an electrically operated strike as defined in claim 10 further including a stop member attached to said bolt member and an opening disposed in said casing, said stop member cooperating with said opening to limit movement of said bolt member between said projected and retracted positions.

t 1 Q i 

1. An electrically operated strike adapted to be mounted on a door frame for controlling opening movements of a door and comprising a casing, a bolt member mounted in said casing and slidable relative thereto between a projected position for engaging a part on the door and a retracted position releasing the part on the door, said casing including a guide surface limiting the movement of said bolt member to a substantially linear direction, spring means biasing said bolt member toward said projected position, electrical means effective when energized to slide said bolt member against the biasing effect of said spring means to said retracted position, and interconnecting means interconnecting said bolt member and said electrical means for sliding said bolt member and through which said spring means and said electrical means act relative to said bolt member, said interconnecting means including dogging means having a dogging position holding said bolt member in said projected position and a release position permitting said bolt member to move toward said retracted position, said dogging means when in said dogging position acting to transfer external forces that may be applied in retracting direction to said bolt member to said casing in a direction transverse to said retracting direction to thereby render said external forces ineffective to retract said bolt member, said electrical means being operable to effect movement of said dogging means to said release position to thereby enable said bolt member to move to said retracted position, said dogging means includinG a plate member pivotably attached to said bolt member and a groove disposed in said casing, said plate member including a shoulder portion engaging said groove when said dogging means is in said dogging position to transfer forces exerted on said bolt member in a transverse direction toward said casing, said plate member being pivotable when said dogging means is in said release position to effect disengagement of said groove and said shoulder portion of said plate member to permit movement of said plate member with said bolt member toward said retracted position.
 2. An electrically operated strike as defined in claim 1 wherein said electrical means includes a solenoid having a plunger and spring means for biasing said plunger toward said bolt and said dogging means further includes a pin attached to said plunger member and movable therewith and an opening disposed in said plate member and through which said pin extends, said spring means biasing said plunger and said pin to engage said opening to pivotably bias said plate member in a first direction to position said shoulder of said plate member in engagement with said groove when said solenoid is deenergized, said pin engaging with said opening and effecting rotation of said plate member in a direction opposite said first direction to remove said shoulder from said groove upon energization of said solenoid to prevent movement of said bolt member inwardly of said casing.
 3. An electrically operated strike as defined in claim 2 further including a stop member disposed in said casing and an opening disposed in said bolt member, said stop member extending into said opening in said bolt member and acting to limit movement of said bolt member between said projected position and said retracted position.
 4. An electrically operated strike adapted to be mounted on a door frame for controlling opening movements of a door and comprising a casing, a bolt member mounted in said casing and slidable relative thereto between a projected position for engaging a part on the door and a retracted position releasing the part on the door, said casing including a guide surface limiting the movement of said bolt member to a substantially linear direction, spring means biasing said bolt member toward said projected position, electrical means effective when energized to slide said bolt member against the biasing effect of said spring means to said retracted position, and interconnecting means interconnecting said bolt member and said electrical means for sliding said bolt member and through which said spring means and said electrical means act relative to said bolt member, said electrical means including a solenoid having a plunger and a spring for biasing said plunger toward said bolt member when said solenoid is deenergized, said interconnecting means including dogging means having a dogging position holding said bolt member in said projected position and a release position permitting said bolt member to move toward said retracted position, said dogging means when in said dogging position acting to transfer external forces that may be applied in retracting direction to said bolt member to said casing in a direction transverse to said retracting direction to thereby render said external forces ineffective to retract said bolt member, said electrical means being operable to effect movement of said dogging means to said release position to thereby enable said bolt member to move to said retracted position, said dogging means including a first plate member attached to said plunger and movable therewith, and a second plate member pivotably mounted on said casing, said second plate being disposed between said first plate member and said bolt member and having a first surface engageable with said bolt member and a second surface opposite said first surface for engaging with said first plate member, said first plate member preventing rotation of said second plate member and acting to hold said first surface of said second plate member in engagement wIth said bolt member to prevent movement of said bolt member toward said retracted position when said solenoid is deenergized, said first plate member disengaging with said second plate member to enable said second plate member to rotate upon energization of said solenoid to enable said bolt member to move toward said retracted position.
 5. An electrically operated strike as defined in claim 4 further including a stop member attached to said bolt member and an opening disposed in said casing, said stop member cooperating with said opening to limit movement of said bolt member between said projecting and retracted positions.
 6. In an electrically operated strike for coacting with a bolt of a door lock, a casing adapted to be mounted on a door frame, a bolt member slidable relatively to a projected position on the casing for engaging the bolt of the door lock, said casing having guide surfaces that support the bolt member for movements in a linear direction while sliding on the casing, a solenoid mounted on said casing and equipped with a spring pressed plunger normally pressing the bolt member to its projected position and sliding the bolt member on its guide surfaces to a retracted position when the solenoid is energized, dogging means movable to position engaging between the bolt member and the casing to dog the bolt member in its projected position, connecting means whereby the solenoid plunger moves the dogging means to dogging position each time the plunger slides the bolt member to projected position, and comprising surfaces through which the spring pressure of the plunger acts to hold said dogging means in dogging position, so that external forces that may be applied to the strike or its bolt member will be ineffective to release the bolt member for sliding away from projected position, the solenoid plunger being effective by said connecting means to move the dogging means to release position when its plunger moves to retract the bolt member.
 7. In an electrically operated strike as defined in claim 6 wherein said dogging means include a plate member pivotably attached to said bolt member and a groove disposed in said casing, said plate member including a shoulder portion engaging said groove when said dogging means is in said dogging position to transfer forces exerted on said bolt member in a transverse direction toward said casing, said plate member being pivotable when said dogging means is in said release position to effect disengagement of said groove and said shoulder portion of said plate member to prevent movement of said plate member with said bolt member toward said retracted position.
 8. In an electrically operated strike as defined in claim 7 wherein said connecting means includes a pin attached to said solenoid plunger and movable therewith and an opening disposed in said plate member and through which said pin extends, said spring pressed plunger acting to bias said pin to engage said opening to pivotably bias said plate member in a first direction to position said shoulder of said plate member in engagement with said groove when said solenoid is deenergized, said pin engaging with said opening and effecting rotation of said plate member in a direction opposite said first direction to remove said shoulder from said groove upon energization of said solenoid to permit movement of said bolt member inwardly of said casing.
 9. In an electrically operated strike as defined in claim 8 further including a stop member disposed in said casing and an opening disposed in said bolt member, said stop member extending into said opening in said bolt member and acting to limit movement of said bolt member between said projected position and said retracted position.
 10. In an electrically operated strike as defined in claim 8 wherein said dogging means includes a first plate member attached to said solenoid plunger and movable therewith, and a second plate member pivotably mounted on said casing, said second plate member being disposed between said first plate member and said bolt member and having a first surface engageable with said bolt member and a second surface opposite said first surface for engaging with said first plate member, said first plate member preventing rotation of said second plate member and acting to hold said first surface of said second plate member in engagement with said bolt member to prevent movement of said bolt member toward said retracted position when said solenoid is deenergized, said first plate member disengaging with said second plate member to enable said second plate member to rotate upon energization of said solenoid to enable said bolt member to move toward said retracted position.
 11. In an electrically operated strike as defined in claim 10 further including a stop member attached to said bolt member and an opening disposed in said casing, said stop member cooperating with said opening to limit movement of said bolt member between said projected and retracted positions. 